Technology for reducing exhaust emissions has become an important issue because various regulations for noxious exhaust emissions of a vehicle have been prepared.
In a diesel engine, a reduction of exhaust emissions is especially important. In particular, particulate matter that is mainly generated by incomplete burning of fuel must be decreased. Various technologies for reducing such particulate matter of a diesel engine have been introduced.
DPF (Diesel Particulate Filter) technology is one of such technologies. In DPF technology, particulate matter is collected by a filter and the collected particulate matter is burned by a burner or a heater.
In DPF technology, a regeneration process for oxidizing the collected matter (e.g., soot) collected by the filter is used. There are various regeneration methods. As an example, there is passive DPF method using an additive, a passive CRT (Continuously Regeneration Trap) method, an active CPF (Catalyzed Particulate Filter) method, and an active DPNR (Diesel Particulate NOx Reduction) method.
The passive method, in which the filter is continuously regenerated when predetermined conditions are satisfied, is not suitable for city driving. Therefore, the active type method, in which exhaust gas is heated during regeneration of the filter by a heater or through fuel injection control, is more relevant for normal vehicles. That is, the CPF method or the DPNR method is more suitable for a vehicle driven primarily in the city.
In the CPF or DPNR methods, regeneration of the DPF is performed while the vehicle is running. The regeneration of the filter is easily performed using exhaust gas when the vehicle is running at a high speed or under a high load. However, when the load is small, the exhaust gas temperature must be increased for the regeneration. In order to increase the temperature of the exhaust gas, the temperature of exhaust gas in a diesel oxidation catalyst (DOC) must be increased through post-injection.
Fuel is consumed for the regeneration of the DPF through the post-injection, so fuel mileage deteriorates. Furthermore, because of late fuel injection timing, fuel is directly injected on a lubricant oil layer on an inner wall of a cylinder, so the oil may be diluted. In addition, because exhaust gas recirculation is not performed during the regeneration process, noxious emissions such as NOx are increased. It is also difficult to determine timing of the generation.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art that is already known to a person skilled in the art.